BIO 115 - Fall Semester 2001
Quiz 2 Grade Key

The answers given below are answers that would qualify for full credit.  Partial credit was given for answers that were on the right track.  Answers are given in red.

Part I:  Define the following terms and specify whether they refer to genotype or phenotype.  (2 pts each, 8 pts total)

Homozygous - an individual with a homozygous genotype has two copies of the same allele at a particular locus (for example, AA or aa)

Heterozygous - an individual with a heterozygous genotype has two different alleles at a particular locus (for example, Aa)

Recessive - a phenotypic trait associated with an allele (for example, b) that is expressed in homozygotes (bb) but not in heterozygotes (Bb)

Dominant - a phenotypic trait associated with an allele (for example, B) that is expressed in homozygotes (BB) and also in heterozygotes (Bb)

Note: The terms recessive and dominant can also refer to the alleles associated with the phenotype.  In the example used above, the allele b would be called a recessive allele and the allele B would be called a dominant allele.  Although common in scientific literature, this usage is not encouraged.  The terms recessive and dominant are best applied to phenotypic traits rather than alleles.

Part II: Define the term natural selection as used in this course (2 pts)

The change in allele frequency that results when there is phenotypic variation in a population, and some of that variation is due to the genotype influencing the phenotype